The present invention relates to a catheter intended to dilate biological ducts, such as occluded and narrowed blood vessels and, more particularly, to a catheter made of an elastic ring whose diameter and force of exertion is controlled by the application of a magnetic field. The elastic ring is able to expand while permitting substantially unchanged flow of fluid, such as blood through the catheter.
Cardiovascular disease is a growing problem in many countries. One of the hallmarks of this disease is the narrowing or occlusion of blood vessels, such as arteries and veins, by the deposition of fats and cholesterol on the walls of these vessels. Balloon catheters are well known in the art for broadening such narrowed or occluded blood vessels. Several types of such balloon catheters are known, all of which have a balloon located at one end of an elastomeric tubule and all of which operate by the same general principles. First, the catheter with the empty, flexible balloon is inserted into the narrowed or occluded blood vessel by using a wire guide. Next, the balloon, which can be ellipsoidal or spherical, is inflated and made rigid as a result of application of water pressure within the catheter. As the balloon is made rigid, it forcibly dilates the narrowed or occluded blood vessel, fractures the deposits of fats or cholesterol on the vessel walls and pushes them aside. This dilation stretches, and often tears, the tissues' fibers in the wall of the blood vessel. With the release of internal pressure within the balloon, it returns to its original diameter while the vessel walls remain laterally displaced and open to blood flow. The catheter, and the balloon at its end, are then removed from the blood vessel.
One important safety factor is the rate of dilation of the blood vessel. A slower rate of dilation is much safer since the tissues' fibers are less likely to tear, and complications, such as a rupture of the blood vessel, are less likely to occur. Thus, a slow rate of dilation is strongly preferable.
Unfortunately, all of these balloon catheters have one major drawback: they substantially block the flow of blood through the blood vessel when the balloon is inflated and made rigid. Such a blockage deprives those tissues supplied by the blood vessel of blood, and hence of oxygen and nutrients, during the period when the balloon is inflated. This deprivation is particularly dangerous for sensitive tissues, which cannot tolerate an interruption in blood supply. Furthermore, such an interruption often causes significant patient discomfort which can even "feel like a heart attack".
In an attempt to solve this problem, a perfusion balloon catheter has been developed for use with blood vessels supplying sensitive tissues. This catheter has openings in the catheter wall before and after the balloon, connected by small tubes passing through the balloon internally, so that blood can perfuse through the catheter. Unfortunately, these openings only permit a small fraction of the blood to flow through the catheter, so that the blood flow is slow and significant patient discomfort is still present. Thus, even using such a perfusion balloon, the catheterization must be done extremely rapidly to avoid damage to sensitive tissues. Furthermore, extremely sensitive tissues, such as the brain, cannot even tolerate such a significant reduction in blood flow, so that blood vessels directly supplying the brain cannot be catheterized. Thus, the perfusion catheter does not adequately solve the problems of balloon catheters, such as the need for rapid dilation of the blood vessel.
However, as noted above, rapid dilation of the blood vessel is undesirable. Such rapid dilation can potentially lead to serious complications, such as rupture of the blood vessel, yet paradoxically, these serious complications must be risked during catheterization to avoid prolonged low blood flow through the vessel.
There is thus a widely recognized need for, and it would be highly advantageous to have, a catheter which can forcibly dilate an occluded or narrowed blood vessel without a substantial reduction in blood flow through the vessel, so that dilation can occur relatively slowly even when the blood vessel is supplying a highly sensitive organ, such as the brain.